Normally my car goes from a garage at home to underground parking at work, so I haven't been having a problem at -25C.
However, during the holidays I did not have that luxury.
My SSD that is the boot drive worked fine at -30C, but my external drive with all the media would not start up.
The solution? I just brought the external drive in the house at night, and I had nice warm toasty tunes in the morning.

In Calgary, we typically only get a few weeks a year of extreme cold, so this is a good compromise for me.

I dont think anything involving heaters is a good idea, especially for things that will turn on and off (hot and cold) constantly like a carpc. It's better to just design something that will run in the cold and keep the system in the cold (eg. trunk).

My carpc is installed in the trunk where it never gets the chance to warm up to cabin temperature. I once made the mistake of leaving the back seat down in -40C while I drove, and after a while, big chunks of snow started to condense on my carpc and dangerously close to the air intake of the case due to the warm cabin air + passengers breathing.

the problem nobb is that most of the consumer pc parts are not designed to run in freezing temperatures. also, every time you run your pc parts of it heats up to 100F and higher... so youre still heat shocking it. its just a brutal environment for computers, anything you can do to relieve stress is a good thing.

I was curious about how other automotive system or mil spec designers go about making products to survive wider temperature ranges and excessive temperature cycling. My line of work allows me to access more research documents than most people can and in my reading it seems that most don't do much to control the temperature that the components see, but work at the low level of system design to make the systems more robust.

Right now my main issue is frost build-up on the motherboard from poor ventilation. One extreme option that I've considered is making a sealed enclosure for the system and filling the entire thing with non-conductive engineered fluid (see link). Modders have been doing something similar to this on a much smaller scale for liquid cooling of GPUs/CPUs.

I was curious about how other automotive system or mil spec designers go about making products to survive wider temperature ranges and excessive temperature cycling. My line of work allows me to access more research documents than most people can and in my reading it seems that most don't do much to control the temperature that the components see, but work at the low level of system design to make the systems more robust.

Right now my main issue is frost build-up on the motherboard from poor ventilation. One extreme option that I've considered is making a sealed enclosure for the system and filling the entire thing with non-conductive engineered fluid (see link). Modders have been doing something similar to this on a much smaller scale for liquid cooling of GPUs/CPUs.

Early (15 or so years ago) liquid cooling solutions for overclocking included putting all of the PC parts in mineral oil. You might try looking at those examples. Here is one example http://www.pugetsystems.com/submerged.php

The easiest way to reduce condensation / frost is increase the airflow. Figure out where to put vents and a couple fans.

What I would suggest is to buy an 8gb compact flash card for your OS and base system, then buy an external HD for your media and everything else. CF cards are not affected by extreme temperatures, so you can leave it in your car during all weather conditions and carry the external HD inside with you. You can buy a cf to ide thing so you can plug the card right into the motherboard. Also cf cards have great boot times.

i think for the most part you can make your computer work comfortably in these weather conditions by:
1) using low power processors (atom, via...etc) and SSD to make little heat as possible to keep the case cool during the summer. Install the PC in the trunk, window tint, and a few case fans will also help keep the heat from your pc.
2) SSD is work well in the cold as well (check the HD extreme cold thread for ones that works well) other than HD most other components works perfectly in hot/cold temperature.

Any other method that actively control the temperature requires a lot of work and almost always requires a constant power source.

My current systems has been working from -31F to +95F (its never hotter than +95 here) without a problem, and has no active component to regulate the temperature.